Cu–Au alloy Schottky junction photodetectors on silicon for sub-bandgap near-infrared detection

Internal photoemission-based plasmonic Schottky diodes fabricated on silicon are promising candidates for near-infrared (NIR) photodetection, particularly for detecting sub-bandgap light beyond silicon’s 1.1 eV threshold. Copper (Cu) offers a cost-effective option but is limited by weak plasmonic performance and susceptibility to oxidation. This study examined the characteristics of CuXAu1−X thin films and investigated the CuXAu1−X/n-Si/Al Schottky photodiodes to enhance Cu NIR detection capabilities. Sequential pulsed laser deposition was employed to prepare alloy films, and x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy were used to analyze the film composition. The efficiency of hot-electron production was greatly enhanced by Au alloying, while pure Cu films showed substantial NIR absorption but poor plasmonic quality parameters. The Schottky barrier height of 0.65 eV for Cu/n-Si and 0.73 eV for Au/n-Si junctions was calculated using the dark I–V measurement. The highest responsivity values recorded were 42.31 mA/W at 1300 nm and 3.65 mA/W at 1550 nm, which surpasses previously reported values for similar devices. A maximum specific detectivity of 6.45 × 1011 Jones was achieved, showing potential for weak light detection. These results show that Cu–Au alloying can improve the optical and electrical properties of Cu in a cost-effective manner. This work presents a new direction to make advanced, low-cost NIR photodetectors.